Anyone ride an Ultimate Wheel?
This is the minimalist setup. Just the wheel and pedals. No frame or seat. I have also seen videos of riders do essentially the same thing on a uni with the front bumper running along on the ground.
How can it be possible?
The seat seems essential to counteract the lean caused by the uneven pressure on the pedals. Yet clearly this is not the case.
Some riders sew “gliding” material on their trousers to allow the tire to rub along their legs without harm. Ideally, the wheel shouldn’t touch the leg, but it’s bound to happen as riding those is clearly beyond all logics.
Freestylers doing that trick are pretty impressive too, and the very short cranks help as the legs don’t travel up and down too much.
I ride an ultimate wheel. I have a 28" wheel that I made out of some nice plywood and an old road bike rim. You can find a lot of posts about UW riding and building on the forum.
In the US you can get nuts threaded for left and right that are the same as the less common 1/2" pedal thread. Using the nuts it’s easy to put a wheel together.
Riding is a lot of work. It’s like the first two weeks of riding a normal unicycle again. All of your weight on the pedals. Feel the burn! Anyway it’s a ton of fun. I have gotten some pretty good distance with mine, and I have a 32" wheel sitting around that one day will be a big UW.
The tire rub is real. The wobble is real. After you get going you can time it so that the wheel stays upright, and doesn’t rub. It’s really hard to ride without any rubbing though.
So definitely not something to be done in shorts. 
After you get somewhat confident you can do it, but my mistake the other day was wearing sandals. The skin on my left ankle is growing back nicely now.
The tire rub was brief and then I got it under control and rode it without any more, but the ankles…
Best to wear inside leg protection, and high shoes that protect your ankles.
As much as the rubbing can be a problem I think the real danger is twisted/broken ankles. I’ve had a couple of UPD’s where the UW came down on my leg, and if I had fallen on the wheel (or even stepped on it) I could have done serious damage.